While the present invention can be used in any suitable marking system, it will be described herein for clarity as used in electrostatic marking systems such as electrophotography or xerography.
Marking systems that transport paper or other media are well known in the art. These marking systems include electrostatic marking systems, non-electrostatic marking systems, printers or any other marking system where paper or other flexible media or sheets are transported internally.
By way of background, in marking systems such as xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor belt or drum surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the belt or drum photoreceptor surface. The toner may be in dry powder form or suspended in a liquid carrier. The charged toner, being electrostatically attached to the latent electrostatic image areas, creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to an intermediate transfer belt or to a final support material such as a paper sheet. When the paper is fed to the system from a paper stack of a feeder mechanism, some papers could be off the home position by many mm, and these fed paper sheets need to be deskewed and laterally registered option (1) into position upon placement on the transport belt or option (2) into position before contacting the image on the photoconductive surface. This is necessary because as the sheets move to the transfer station and approach the imaged photoconductor surface, they need to be in perfect alignment with the toned image on the photoconductive layer for proper image transfer to the sheet to take place. Also, many paper-moving systems are used for transporting printed sheets so they may be formed into books and the like. The present invention is useful in marking systems in both pre and post paper transport systems.
In the present system a number of sensors evaluate the positioning of the sheet as the paper sheet makes initial contact and when it continues down the transport path, and convey this information to a controller that will regulate and control progression of the sheet (including lateral registration) before it reaches the finishing station or the imaged photoconductive surface for image transfer to the sheet. In high speed marking systems, reaction and action time is important. Some prior art registration systems are too slow to be useful in today's high speed systems. The present invention allows for lateral reset while the paper lead edge is present in the gripper means.
In recent years, most of the media transport devices use nip rolls and a corresponding baffle system. Due to the nature of tolerance variations on those parts, there is slippage skew and walk observed which require an “in-line” additional registration subsystem to correct errors. Often these in line subsystems have been found to be inadequate.